Estimate gravel, perforated pipe, filter fabric, excavation, weight, and optional cost for a simple French drain using dimensions supplied by your project design.
The trench is modeled as a rectangular prism. A custom gravel zone can include material below and above the pipe, and the pipe’s outside cylinder can be subtracted from gravel volume.
Project gravel waste and pipe extra are applied separately after included runs are summed.
excavation = length × width × trench depthgravel depth = below-pipe gravel + pipe outside diameter + above-pipe gravelpipe volume = π × (outside diameter ÷ 2)² × pipe lengthplanning gravel = (gross gravel zone − pipe displacement) × (1 + waste rate)bottom + sides = width + 2 × gravel depth; full wrap = 2 × width + 2 × gravel depth + overlapA 100 × 1 × 2 ft full-fill trench starts with 200 ft³ of gravel-zone volume before subtracting 4-in outside-diameter pipe displacement and applying waste.
With 6 in below, 4 in pipe, and 6 in above, the gravel zone is 16 in deep.
A 100 ft drain with 10% pipe extra requires 110 ft; 10 ft stock sections require 11 pieces.
A 1 ft trench with a 1.5 ft gravel zone requires 4 ft-wide fabric for bottom plus both sides.
Only the pipe’s external cylinder displaces gravel; internal pipe volume is not subtracted.
Gravel weight varies by material and moisture, so density is optional and user supplied.
Gravel waste, pipe extra, and fabric waste are applied independently once.
A fabric roll narrower than the calculated wrap width may require seams or another layout.
Custom vertical layout counts only the entered gravel envelope. Remaining trench depth is treated as unspecified backfill, not gravel.
The fabric estimate models bottom and sides or a full wrap. Roll calculation uses drain length when roll width can cover the required cross-section.
Optional density converts planning volume to mass. Bag quantities use manufacturer volume yield; weight purchasing requires density.
Gross bank excavation and optional swell are estimates. An entered slope percentage produces elevation drop only and is not a recommendation.
This calculator does not determine suitability, slope, diameter, outlet design, hydraulic capacity, infiltration, groundwater control, waterproofing, or code compliance.
Calculate the gravel envelope, subtract optional outside-pipe displacement, then add the selected project waste.
Multiply drain length, trench width, and gravel-zone depth, then subtract pipe displacement where appropriate.
Base pipe length equals included drain lengths; add the selected pipe extra separately.
Yes when the outside of the pipe occupies the gravel envelope; the option can be disabled when it does not.
The calculator does not prescribe this; enter the depth required by your project design.
Enter the design depth and ensure the complete vertical gravel zone fits the trench.
Multiply the required cross-section wrap width by drain length and add fabric waste.
Bottom plus sides uses trench width plus twice gravel depth; a full wrap also includes the top and overlap.
The result converts the unrounded planning volume to cubic yards.
Weight requires an approximate supplier or material density.
Multiply trench length, width, and depth.
This calculator does not prescribe slope; it only computes drop from a slope entered by the user.
The calculator does not select pipe diameter or drainage capacity.
No. Hydraulic and site design require project-specific evaluation.